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Bundled/Grouped Cables in Concealed Spaces
The Maine State Fire Sprinkler Technical Policy states in Part 2, item 7: “Non-combustible/limited-combustible concealed spaces having 15 or more combustible electrical cables grouped together such as in cable trays, shall be sprinklered in the area of the cables in NFPA 13 fire sprinkler systems. Plenum-rated and riser-rated telecommunication cables however are considered to be limited combustible/fire resistive according to standards established by NFPA 70 and therefore do not trigger this fire sprinkler requirement.”
Here is the background. NFPA 13, (2010 edition), requires fire sprinkler coverage throughout a building, with only a few exceptions for certain spaces. Concealed, non-combustible spaces that are not used for storage or occupancy meet one of these exceptions. This comes from section 220.127.116.11.1. The question then arises, “Can there be minor amounts of combustible material in the concealed space and still meet the exception?” The answer is “Yes”. So then the next question is “When is the amount too much?”
The annex note addresses this and reads, “Minor quantities of combustible materials such as but not limited to: cabling, nonmetallic plumbing piping, non-structural wood, etc. can be present in concealed spaces constructed of limited or noncombustible materials but should not typically be viewed as requiring sprinklers…For example, it is not the intent of this section to require sprinklers, which would not otherwise be required, in the interstitial space of a typical office building solely due to the presence of the usual amount of cabling within the space. The threshold value at which sprinklers become necessary in the concealed space is not defined”. Many years ago, Factory Mutual Insurance Company had a rule of thumb that 15 cables bundled together as being too much. The State adopted this rule of thumb into its fire sprinkler technical policy. The bundling/grouping of combustible cables creates a concentrated fuel load.
If you do have combustible cables bundled into groups of 15 or more, then only that area of the concealed space, (such as a cable tray), will require fire sprinkler protection according to Section 18.104.22.168.
In summary, if all of the cable in a cable tray or bundle is plenum and/or riser rated, then that does not trigger the requirement for fire sprinkler protection in the concealed space. There can also be up to and including 14 combustible cables in the group without triggering the requirement for fire sprinkler protection.
[Last updated 1-11-12 to reflect currently adopted codes & standards. This was previously edited 1-15-09 to correct minor typos, but content then was not changed since it was first posted 9-4-07.]
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